Between elm and black walnut, I'd choose black walnut. It's properties are similar to yew (mass weight, recovery, draw force curve) and it looks really nice too. Chek-Mate doesn't offer bamboo because, in their testing, they found no benefits to it over yew, plus it costs more, is harder to work with, and is not as durable in the long run.

The double tapered core isn't available in the recurves, just the Crusader, and the two flatbows--it won't work the same in a recurve.

Troy did bring up a good point--if the glass isn't perfect (and it's very hard to tell until the limbs are glued up), the darker woods will show any imperfections more than lighter woods.

To me, yew is the ultimate limb wood, but walnut is a fairly close second. Marc refers to it as "poor man's yew".

Chad